I read in Russian popular articles that it is allowed to preserve herring/fish with Hexamethylenetetramine in Europe. Since Soviet times, I like to buy salty herring and marinade it with Vinegar. The food-safety article says that Hexamethylenetetramine + Vinegar = Formaldehyde, which is a serious poison.
How can I easily test presence of Hexamethylenetetramine or Formaldehyde in food?
The salty herring that I buy is sold loosely, without packaging, so that I cannot simply read the ingredients.